The physical properties (phase, size, morphology) of nickel metal nanoparticles (Ni-NPs) can have a dramatic impact on their properties. Ni-NPs have been isolated in either the face-centered cubic (fcc) or metastable hexagonal closed packed (hcp) structure, which reportedly alters their magnetic properties: fcc Ni-NPs have exhibited ˜30 times stronger M-H data compared to the hcp Ni-NPs. See M. Richard-Plouet et al., Chem. Mater. 19, 865 (2007); M. Han et al., Adv. Mater. 19, 1096 (2007); C. N. Chinnasamy et al., J. Appl. Phys. 97, 10J309 (2005); and J. Gong et al., J. Alloys Compd. 457, 6 (2008). Additionally, the size of the Ni—NP imparts different final properties: 15 nm Ni-NPs are superparamagnetic with magnetic saturation 2% less than bulk Ni0, whereas 20 nm and larger Ni-NPs are ferromagnetic. See S. Carenco et al., Chem. Mater. 22, 1340 (2010); and B. Tanushree et al., Nanotechnology 20, 415603 (2009). Morphology also plays a role in the final properties, with cube-shaped Ni-NPs reportedly demonstrating 10 times more magnetic saturation than spherical nanoparticles of the same size. See A. P. LaGrow et al., J. Am. Chem. Soc. 134, 855 (2012). Therefore, controlling the crystalline phase, size, and morphology is critical in order to tailor the final properties of Ni-NPs.
Several synthetic routes are available for the production of Ni-NPs, including pyrolysis, sputtering, reversed micelles, and aqueous/non-aqueous chemical reduction routes. See Y. He et al., Chem. Mater. 17, 1017 (2005); G. Ausanio et al., Appl. Phys. Lett. 85, 4103 (2004); G. B. Thompson et al., Acta Mater. 50, 643 (2002); D.-H. Chen and S.-H. Wu, Chem. Mater. 12, 1354 (2000); M. Han et al., Adv. Mater. 19, 1096 (2007); L. Yonghua et al., Nanotechnology 17, 1797 (2006); N. Cordente et al., Nano Lett. 1, 565 (2001); and Y. Chen et al., J. Nanosci. Nanotechnol. 9, 5157 (2009). The majority of these research efforts have focused on altering the Ni—NP properties by varying the surfactant and monomer concentration. The precursors used are often commercially available (i.e., halides, acetates, and nitrates), with particular attention paid to nickel acetylacetonate for the production of spherical and cube Ni-NPs. See M. Green and P. O'Brien, Chem. Commun. (Cambridge, U. K.), 1912 (2001); Y. Hou and S. Gao, J. Mater. Chem. 13, 1510 (2003); M. L. Singla et al., Appl. Catal., A 323, 51 (2007); S.-H. Wu and D.-H. Chen, J. Colloid Interface Sci. 259, 282 (2003); L. Chen et al., Mater. Sci. Eng., A 452-453, 262 (2007); A. Wang et al., Catal. Commun. 10, 2060 (2009); K. J. Carroll et al., J. Phys. Chem. C 115, 2656 (2011); S. Mourdikoudis et al., J. Magn. Magn. Mater. 321, 2723 (2009); J. Gong et al., J. Alloys Compd. 457, 6 (2008); V. Tzitzios et al., Nanotechnology 17, 3750 (2006); S. Carenco et al., Chem. Mater. 22, 1340 (2010); A. P. LaGrow et al., J. Am. Chem. Soc. 134, 855 (2012); Y. Chen et al., J. Nanosci. Nanotechnol. 9, 5157 (2009); O. Pascu et al., Langmuir 26, 12548 (2010); and C. Yuanzhi et al., Nanotechnology 18, 505703 (2007). Some efforts have explored the use of tailored precursors such as nickel 1,5-cyclooctadiene or oleate which generate Ni0 nanorods (˜12-17 nm) or petal-like nanomaterials (15-20 nm), respectively. See N. Cordente et al., Nano Lett. 1, 565 (2001); and M. Han et al., Adv. Mater. 19, 1096 (2007).
However, a need remains for precursors that have utility in the generation of nickel metal nanoparticles.